To understand epidemics of Fusarium head blight of wheat, we investigated the distribution of symptomatic wheat heads in a field at four times, from the first detection of the disease and then every 4 days after. The distribution of diseased heads within a field was analyzed using the Morisita index of spatial-distribution patterns. The distribution patterns of diseased heads were similar between experiments in 2004 and 2006. New diseased heads were observed 14–34 days after anthesis. The degree of clustering of diseased heads based on the Morisita index did not increase with time, but the significance of the cluster distribution did increase, suggesting that populations of the pathogen formed new independent points of clustering during the investigation. Therefore, during the life cycle of the pathogen, ascospores from the primary inoculum render new infections over long periods in fields, and conidia have a limited role in secondary infections in the disease cycle.

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To generate a causal hypothesis for an association between the disease severity of Alternaria blotch of apple before early July and subsequent severity in late July, a nested case-control study was carried out using 13 years of severity data (1993-2005) from Iwate Prefecture, Japan. The data consisted of 625 cases in 40-56 orchards, and each case included data of leaf disease severity from early June to late July. The cases were stratified into four geographic groups to eliminate confounding factors from climate and epidemic characteristics. Preliminary analysis indicated that one geographic group was considered at low risk for severe epidemics, and the rest were rated as high risk. The results showed that initial disease development in early July was closely related to the occurrence of severe epidemics in late July in both risk groups, where the odds ratio (OR) of the low-risk group was 10.4 and that of the high-risk group was 3.1. The relationships between the initial disease development in late June and the severe epidemics of the disease in late July were not statistically significant in the high-risk group but in the low-risk group, the OR was 3.8. The results reveal a highly probable causality between disease severity at the early and at the late phases of the epidemics under conventional orchard management.

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Sweet potato feathery mottle virus (SPFMV) can cause russet cracks and reduce yields of storage roots of Ipomoea batatas, which are used for food and production spirit production. When I. batatas was pretreated with a protective mild isolate (designated as 10-O) of SPFMV, obtained from I. batatas in Oita Prefecture, yields were not reduced and fewer russet cracks developed after subsequent inoculation with SPFMV-S, a severe strain of SPFMV. In addition, treatment with 10-O alone did not affect either the nutritional value of the storage roots or the processing suitability of sweetpotato. The nutritional components and the spirits produced by the healthy and the 10-O-infected I. batatas did not differ. Moreover, plants that were infected with 10-O grew longer roots, resulting in an improvement in the heat conduction and the processing efficiency. Thus, 10-O is a useful agent for controlling russet crack diseases and for improving the processing suitability of sweetpotato.

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The influence of yeast spot disease caused by Eremothecium coryli and E. ashbyi on the development of soybean seed was investigated. Soybean seeds were inoculated with one of the yeasts via sucking by Riptortus pedestris, allowed to feed on the seeds for 24 hours at room temperature. As a result, the seed coats of inoculated seeds developed necrotic areas, and seed filling of the seeds was inhibited. The symptoms and degree of inhibition of the infected seeds differed significantly from those on soybean seeds that had been sucked by yeast-free R. pedestris.

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